From owner-freebsd-arch Sun Oct 13 19:19:57 2002 Delivered-To: freebsd-arch@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 7267F37B401 for ; Sun, 13 Oct 2002 19:19:56 -0700 (PDT) Received: from softweyr.com (softweyr.com [65.88.244.127]) by mx1.FreeBSD.org (Postfix) with ESMTP id A4E9443EB7 for ; Sun, 13 Oct 2002 19:19:55 -0700 (PDT) (envelope-from wes@softweyr.com) Received: from nextgig-11.access.nethere.net ([66.63.140.203] helo=softweyr.com) by softweyr.com with esmtp (Exim 3.35 #1) id 180uoP-0006e0-00; Sun, 13 Oct 2002 20:18:29 -0600 Message-ID: <3DAA2C4F.9E15CA75@softweyr.com> Date: Sun, 13 Oct 2002 19:30:39 -0700 From: Wes Peters Organization: Softweyr LLC X-Mailer: Mozilla 4.78 [en] (X11; U; Linux 2.4.2 i386) X-Accept-Language: en MIME-Version: 1.0 To: Terry Lambert Cc: ticso@cicely.de, "M. Warner Losh" , hch@infradead.org, dillon@apollo.backplane.com, vova@sw.ru, nate@root.org, arch@FreeBSD.org Subject: Re: Database indexes and ram References: <3DA954CF.98B0891A@mindspring.com> <20021013.060851.113437955.imp@bsdimp.com> <3DA9B4A8.194A02FC@mindspring.com> <20021013.120847.31902907.imp@bsdimp.com> <20021013181633.GB34517@cicely8.cicely.de> <3DA9C3B9.E78BBFE6@mindspring.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Terry Lambert wrote: > > Bernd Walter wrote: > > Of course they can do. > > It's just a matter if the card and the board support 2 address cycles. > > Or if the board can map the pci reachable space - as alphas can do. > > The question is whether you can say reliably that all cards that > will be sharing cached data space can do this, or whether you > will have to bounce the data to below 4G. > > If you can't *know*, then to ensure operation, you *must* bounce > the data to proactively guarantee that the physical address will > be in range of the card's DMA engine. > > Among other things, this means recognizing a 32 bit card in a 64 > bit slot, and a 64 bit card in a 32 bit slot, and a 64 bit card > in a 64 bit slot, but which has only 32 bits worth of electrical > connector on the physical card. > > If you can guarantee that, then you can do it without bouncing. > > Can you do that? No, and that's exactly why the Linux developers took the tack they did: all of the DMA targets are allocated in the lower 4GB of physical address space. It was quite an intelligent decision, one that made me grin when I "got it." -- "Where am I, and what am I doing in this handbasket?" Wes Peters Softweyr LLC wes@softweyr.com http://softweyr.com/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message